Open AccessHigh‐resolution observations of the near‐infrared emission from NGC 6822 Hubble V
Author(s) -
Lee Sungho,
Pak Soojong,
Lee SangGak,
Davis Christopher J.,
Kaufman Michael J.,
Mochizuki Kenji,
Jaffe Daniel T.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.09259.x
Subject(s) - physics , astrophysics , galaxy , emission spectrum , infrared , line (geometry) , interstellar medium , excited state , molecular cloud , metallicity , astronomy , collisional excitation , ionization , h ii region , star formation , spectral line , atomic physics , stars , ion , geometry , mathematics , quantum mechanics
We have observed Hubble V, the brightest H ii region complex in the dwarf irregular galaxy NGC 6822, at near‐infrared (near‐IR; 1.8–2.4 μm) wavelengths. The line emission maps of Hubble V show the typical structure of a photodissociation region (PDR) where an ionized core, traced by compact He i emission (2.0587 μm) and Brγ emission (2.1661 μm), is surrounded by an outer layer traced by molecular hydrogen (H 2 ) emission. The measured line ratios of H 2 2–1 S(1) (2.2477 μm)/1–0 S(1) (2.1218 μm) from 0.2 to 0.6 and the unshifted and unresolved line profiles suggest that the H 2 emission originates purely from a PDR. We find no evidence for shock activity. By comparing the H 2 results with a PDR model, we conclude that Hubble V includes dense (10 4.5 cm −3 ) and warm PDRs. In this environment, most of the H 2 molecules are excited by far‐ultraviolet photons (with a field strength of 10 2–4 times that of the average interstellar field), although collisional processes de‐excite H 2 and contribute significantly to the excitation of the first vibrational level. We expect that Hubble V is in the early stage of molecular cloud dissolution.